Chemistry Reference
In-Depth Information
controlled conditions, exert microfloral changes and result in various amounts of
short chain fatty acid (SCFA) production in comparison with controls.
3
These crite-
ria have been translated into a Prebiotic Index (PI).
The PI is a description of the relative efficiency of particular molecule(s) to
increase absolute numbers of bifidobacteria and lactobacilli while subtracting any
expansive effects on bacteroides and clostridia. Increases in the lactic acid bacteria
are desirable, whereas increases in the other two may not be. The magnitude of
bacterial change depends on the numbers present in the host colon prior to introduc-
tion of the compound.
2
In this schema, lactulose compared with control has a PI of
4.66 (control 1.23) and lactose 5.75 (control 1.02).
3
By comparison, the bimolecular
fructo-oligosaccharide is listed to have a PI of 7.64. Lactitol or any of the sugar alco-
hols are not listed. Whether the length of time a particular prebiotic is ingested alters
effects is unclear. For example, are there quantitative or even qualitative differences
between ingestion of a particular prebiotic for 1, 6, 12 months, or half a lifetime?
In addition, short chain fatty acids produced from disaccharides may have inde-
pendent antiinflammatory effects. It has been known for some time that butyrate
is the preferred nutrient of colonocytes and exerts antiinflammatory and possible
antineoplastic effects. Recently, similar attributes of cytokine inhibition and anti-
inflammatory effects for acetate and propionate were reported in an
in vitro
model.
4
As discussed, for each disaccharide, a number of well-defined human health ben-
efits are attributed to them. Therefore, with the exception of lactulose, which is rec-
ognized as a prebiotic, perhaps a new definition needs to be developed for lactitol and
lactose, or the concept of prebiotic needs to be again reassessed. All three certainly
should be considered functional food components.
5.2
lACTulosE
The disaccharide lactulose was first manufactured from lactose in 1930,
6
and
although not a natural product, it forms in small amounts by noncatalytic isomeriza-
tion when milk is heat-treated. The product 4-
O
-β-d-galactopyranosyl-d-fructose
has the identical empirical formula as for lactose (C
12
H
22
O
11
). Industrial production
of the sugar requires alkali hydroxides and boric acid.
7
However, biological manu-
facture of lactulose is also possible through transgalactosylation from lactose using
β-galactosidase from
Aspergillus oryzae
and from
Pyrococcus furiosus
.
8
The end
product is available as a liquid syrup or in crystalline form.
5. 2 .1
Physiological and Prebiotic Effects of lactulose
Lactulose is not digested by human intestinal enzymes and, therefore, reaches
the lower bowel making it available for bacterial metabolism. A very small amount
is absorbed in healthy subjects through tight junctions between cells. Approximately
0.4 to 2 percent may be absorbed in this way under normal conditions.
9
As membrane
permeability changes, more disaccharide is absorbed via this route and excreted
intact into urine.
